U.S. patent application number 10/677178 was filed with the patent office on 2004-04-15 for test apparatus for testing substrates at low temperatures.
Invention is credited to Dietrich, Claus, Kiesewetter, Jorg, Schmidt, Axel, Schneidewind, Stefan, Werner, Hans-Michael, Zieger, Matthias.
Application Number | 20040070415 10/677178 |
Document ID | / |
Family ID | 32070711 |
Filed Date | 2004-04-15 |
United States Patent
Application |
20040070415 |
Kind Code |
A1 |
Schneidewind, Stefan ; et
al. |
April 15, 2004 |
Test apparatus for testing substrates at low temperatures
Abstract
A test apparatuss for testing substrates at low temperatures has
a chuck, which can be displaced in the working area by means of a
chuck drive, the temperature of which can be controlled using
heating and cooling means. The chuck has a receiving surface for
receiving a test substrate and holding means for fixing a substrate
carrier which receives the test substrate. Spatially and thermally
defined test conditions are maintained with minimal energy and
labor costs both at room temperatures and at low temperatures. This
is achieved by providing a vacuum chamber which surrounds the
working area of the chuck. The chuck is on one side thermally
decoupled from the uncooled chuck drive and on the other side is
thermally connected in a releasable manner to the test substrate.
The cooled chuck and the cooled test substrate are shielded from
the thermal radiation of the surrounding uncooled assemblies by
means of a directly cooled thermal radiation shield.
Inventors: |
Schneidewind, Stefan;
(Reichenberg, DE) ; Dietrich, Claus; (Sacka,
DE) ; Kiesewetter, Jorg; (Dresden, DE) ;
Werner, Hans-Michael; (Dresden, DE) ; Schmidt,
Axel; (Stolpchen, DE) ; Zieger, Matthias;
(Riesa, DE) |
Correspondence
Address: |
BAKER & BOTTS
30 ROCKEFELLER PLAZA
NEW YORK
NY
10112
|
Family ID: |
32070711 |
Appl. No.: |
10/677178 |
Filed: |
October 2, 2003 |
Current U.S.
Class: |
324/750.03 |
Current CPC
Class: |
G01R 31/2806 20130101;
G01R 31/2887 20130101; G01R 31/2865 20130101; G01R 31/2831
20130101 |
Class at
Publication: |
324/760 |
International
Class: |
G01R 031/02 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 2, 2002 |
DE |
102 46 282.8 |
Oct 2, 2002 |
DE |
102 46 232.1 |
Claims
We claim:
1. A test apparatus for testing substrates at low temperatures,
comprising: a vacuum chamber; an uncooled chuck drive arranged
within said vacuum chamber; a chuck carried by said chuck drive and
thermally decoupled therefrom, said chuck having a receiving
surface for receiving a test substrate; a substrate carrier for
receiving and holding a substrate to be tested in releasable
thermal contact with said receiving surface; and a directly cooled
thermal radiation shield arranged to shield said test substrate
from thermal radiation.
2. The test apparatus as claimed in claim 1 wherein said vacuum
chamber is provided with an inspection opening on top wall lying
opposite a top side of said chuck.
3. The test apparatus as claimed in claim 1 wherein said chuck is
connected to said chuck drive by means of an intermediate part made
from a material with a lower thermal conductivity than metal.
4. The test apparatus as claimed in one of claims 1 wherein said
thermal radiation shield has a through-opening in the center.
5. The test apparatus as claimed in claim 4, wherein the
through-opening is provided with a transparent closure which
filters light of selected wavelengths.
6. The test apparatus as claimed in claim 1 wherein there are
provided probe holders which are thermally conductively connected
to the chuck.
7. The test apparatus as claimed in claim 1 wherein there are
provided probe holders which are thermally conductively connected
to the thermal radiation shield.
8. The test apparatus as claimed in claims 1 wherein said substrate
carrier is carried by a mounting arrangement which includes a
vertically movable member which is thermally connected to the
cooled chuck, and a holding pin, which is mounted to the chuck
drive and consists of a material with a lower thermal conductivity
than metal.
9. The test apparatus as claimed in claim 1 wherein the chuck
comprises a chuck body with a chuck surface and a chuck plate which
rests on the chuck surface over its entire area and can be detached
from the chuck body.
10. The test apparatus as claimed in claim 1 wherein cooled parts
of the chuck and of the thermal radiation shield consist of
material with a good thermal conductivity, and the cooled parts of
the chuck have highly reflective surfaces.
11. The test apparatus as claimed in claim 1 wherein the chuck has
a chuck heater,
12. The test apparatus as claimed in claim 1 wherein the thermal
radiation shield has a shield heater.
Description
BACKGROUND OF THE INVENTION
[0001] This application is related to the subject matter of
commonly owned, co-pending application Serial No. ______, filed on
even date herewith, the specification of which is incorporated
herein by reference.
[0002] The invention relates to a test apparatus for testing
substrates at low temperatures, having a chuck, which can be
displaced in the working area by means of a chuck drive and can be
cooled using suitable cooling apparatus. The test apparatus
includes a receiving surface for receiving a test substrate,
comprising a substrate carrier and component to be tested, and a
holding arrangement for receiving the substrate carrier.
[0003] The test substrate may comprise either semiconductor chips
which are still joined to the wafer, or individual components, such
as semiconductor chips, hybrid components, micromechanical
components or the like. The substrate has a smooth and planar
underside and is arranged and held, at least indirectly, on the
chuck, which has a smooth and planar receiving surface. The test
substrate can be displaced with the chuck in the working area by
means of a chuck drive, so that it can be positioned in relation to
the contact-making needles. Positioning in the horizontal plane is
generally effected by an X-Y table, which also an orientation angle
adjustment in the range of a few degrees.
[0004] The operational reliability of electronic components is
preferably tested under the environmental conditions which
correspond to the conditions of use of the component in question.
In this context, testing at temperatures below the freezing point
of water is a focal point.
[0005] To set these test conditions, the working area of the test
apparatus is generally surrounded by an enclosure. A test apparatus
having a housing of this type is known from DE 4109908 C2. In the
case of this test apparatus, the enclosure has a plurality of inlet
openings in the lower section and a further opening, which serves
both as an outlet opening and to provide test probe access in the
upper wall of the enclosure. When testing in the relatively
low-temperature range, a gas flow is provided through the working
area by means of these openings, in order to prevent the
precipitation of moisture from the surrounding atmosphere on the
test substrate. However, these test conditions restrict the
possible low temperature range for the testing of electronic
components.
[0006] In addition to receiving and positioning the test substrate,
the chuck is also used to set the temperature at which the testing
of the test substrate is to take place. For this purpose, a
suitable coolant is applied to the chuck. To set the temperature or
further controlled test conditions at the chuck, the latter is
connected, via fluid lines, to the corresponding coolant source
located outside the working area. On account of heat exchange with
the chuck drive, which is in thermal contact with the chuck, the
chuck drive is likewise cooled. In the test apparatus described,
the cooled chuck drive constitutes a particular drawback, since the
positioning of the chuck relative to the probes can only be
effected with the reproducibility and accuracy required for the
test substrate with considerable outlay on time and labor. The
media connections and lines, which are relatively rigid at
relatively low temperatures, further exacerbate this drawback.
[0007] A further drawback consists in the fact that the temperature
of the test substrate is influenced by the surrounding components
of the test apparatus, the temperature of which has been set very
differently by the various heat exchange processes in the
equilibrium state. For example, high levels of heat are introduced
into the test substrate as a result of uncontrollable thermal
radiation and convection from the surrounding hot components, which
has a significant adverse effect on the accuracy and
reproducibility of the testing.
[0008] For the testing to be carried out, the test substrate has
test probes applied to it, in the form of contact-making needles
with electrical input signals, and the output signals are measured
using additional probes. The output signals may be of various types
and may also be produced by other input variables, such as for
example radiation in different wavelength regions. The probes are
generally located outside the working area, on the upper housing
closure, and make contact with the components through the
above-described opening located in the top of the housing, either
directly or indirectly via contact-making surfaces which are
present on the test substrate. When the components are being tested
at relatively low temperatures, the fact that the probes are at
room temperature firstly means that the geometry of the probes does
not coincide with the geometry of the test substrates in the cooled
state. Secondly, the contact between the test substrate and the
warmer probes leads to a temperature drift at the substrate and
therefore to a change in the test conditions. These facts also have
a significant adverse effect on the accuracy and reproducibility of
the testing at relatively low temperatures.
[0009] Accordingly, the invention is based on the object of
providing a test apparatus for testing substrates at low
temperatures in which spatially and thermally defined test
conditions can be set and maintained with minimal outlay on energy
and labor both at room temperatures and at low temperatures.
SUMMARY OF THE INVENTION
[0010] According to the invention, the object is achieved by virtue
of the fact that there is a vacuum chamber which surrounds the
working area of the chuck and is connected to a vacuum pump, and
that one side of the chuck is thermally decoupled from the uncooled
chuck drive and the other side of the chuck is thermally connected
in a releasable manner to the test substrate. The test substrate is
shielded from the thermal radiation of the surrounding uncooled
assemblies by means of a directly cooled thermal radiation shield.
The production of a vacuum in the working area makes it possible to
test more components than were described in the introduction. In
particular, it is now possible to test the oscillation behavior of
micromechanical components or optical switches, since the presence
of immobile and moving gases in the test environment influences the
oscillation behavior of the components themselves or causes
oscillations in the test atmosphere to be superimposed on the test
variable.
[0011] The thermal decoupling of the chuck drive from the cooled
chuck allows a motorized X-Y table to be used as a chuck drive,
even at very low temperatures. Consequently, the chuck drive can be
controlled very easily by an operating element outside the vacuum
chamber, and the mobility of the X-Y table is not restricted by the
low temperature of the moving parts. Furthermore, the stepper
motors of the X-Y table allow the chuck to be positioned with an
accuracy and reproducibility of a few micrometers without problems
despite the presence of rigid coolant lines.
[0012] Furthermore, the thermal decoupling of the chuck, together
with a reduction in the number of components to be cooled, leads to
an increase in the stability and accuracy of the temperature regime
and to a reduction in the coolant consumption. By virtue of the
fact that heat exchange with the environment through convection is
prevented, in particular the production of a vacuum in the working
area accelerates the cooling process.
[0013] Testing of the components at low temperatures under vacuum
conditions is particularly advantageous, since in vacuo no
moisture, which would otherwise distort the test results or prevent
testing altogether, is precipitated on the test substrate. The
precipitation of moisture during evacuation is prevented by a
suitable dry working gas being introduced into the vacuum chamber
beforehand.
[0014] Optimum cooling of the test substrate is achieved by virtue
of the fact that the substrate is provided with a planar, smooth
underside and rests on the chuck over its entire surface, the chuck
likewise having a planar, smooth receiving surface, and a
non-positive connection being produced between these two surfaces
by suitable holding means, in such a manner that this connection
can be released for the purpose of mounting the test substrate on
the chuck.
[0015] To reduce the introduction of heat at the chuck and at the
test substrate from the warmer surrounding components of the test
apparatus via thermal radiation, these components are shielded by a
thermal radiation shield. It is expedient for the thermal radiation
shield to be cooled directly to the chuck temperature by the
application of the coolant which is in each case being used.
[0016] The cooling of the chuck and the thermal radiation shield
can take place in various ways in the cooling regime, depending on
the requirements and optimal conditions of the testing process. By
way of example, the testing process can be shortened if the chuck
and the test substrate are cooled first of all, and then the
thermal radiation shield is cooled, since in this way the testing
of the components can be commenced even before the final
temperature of the thermal radiation shield is reached.
Precipitation of moisture on the test substrate is avoided by
virtue of the fact that dry nitrogen is admitted before the vacuum
chamber is evacuated. If the thermal radiation shield is cooled
first of all, followed by the chuck with the test substrate, any
moisture which may be present will precipitate on the thermal
radiation shield rather than on the substrate, so that the testing
is not influenced. The simultaneous cooling of the chuck and the
thermal radiation shield not only prevents the precipitation of
moisture but also prevents any distortion from occurring in the
test assembly, which significantly improves the accuracy of
positioning of the test probes.
[0017] In one expedient configuration of the invention, the vacuum
chamber is provided with an inspection opening on the top side
lying opposite the top side of the chuck. This makes it possible to
observe on the one hand the test operation and on the other hand
the positioning, which is important in particular when testing
individual components.
[0018] The thermal decoupling of the chuck is achieved in
particular by virtue of the fact that, according to an advantageous
embodiment of the invention, the chuck is connected to the X-Y
table by means of an intermediate part made from a material with a
lower thermal conductivity than metal. Decoupling of this nature
causes the temperature of the chuck and therefore of the test
substrate to follow the boiling point of the coolant with a high
level of accuracy and stability, since apart from the test
substrate no further parts are cooled indirectly.
[0019] According to a further embodiment of the invention, the
thermal radiation shield has a through-opening in the center. This,
like the inspection opening in the vacuum chamber, allows the
positioning and testing of the test substrate to be observed.
Furthermore, it is possible to arrange the probe holders above the
thermal radiation shield and for the probes to be brought into
contact with the test substrate through this opening.
[0020] It is also possible for this through-opening to be provided
with a transparent closure which filters light of selected
wavelengths. This has the advantage of enabling further components
to be tested, such as in particular sensors for radiation of this
defined wavelength. The filter makes it possible to prevent the
testing from being influenced by precisely this background
radiation.
[0021] In one expedient refinement of the invention, the test
substrate is provided with probe holders for individual and
multiple probes, which are thermally conductively connected to the
chuck. This causes the temperature of the probes to track the chuck
temperature and eliminates the need for readjustment of the probes
in the cooled state, since the positioning of the individual probes
relative to the components and the distances between the multiple
probes, which are matched to the distances between the components
on the test substrate, do not change or only change slightly during
cooling. Furthermore, the introduction of heat by the warmer probes
and therefore the temperature drift at the component are
prevented.
[0022] In the case of various geometries of the test substrate, it
is expedient for the probe holders not to be directly connected to
the test substrate itself. Therefore, in a further configuration of
the invention, the thermal radiation shield is at least indirectly
provided with the probe holders for individual or multiple probes
in such a manner that these probes are thermally conductively
connected to the thermal radiation shield. Since, as described, the
thermal radiation shield is cooled directly by the application of
coolant, in this embodiment too, the temperature of the probes
tracks that of the test substrate. There is no need for
readjustment, as would be necessary as a result of thermally
induced changes in the test substrate and probe geometries and the
above-described temperature drift of the component.
[0023] In an advantageous configuration of the invention, the
holding arrangement for the substrate carrier has a vertically
movable head, which is thermally connected to the cooled chuck in
the part close to the substrate, and a holding pin which is fixed
to the X-Y table. The holding pin consists of a material with a
lower thermal conductivity than metal.
[0024] Forming the holding arrangement from two parts, the head and
the holding pin, firstly allows the heads to be cooled indirectly
via the cooled chuck, on account of the use of a material of good
thermal conductivity for these heads, and secondly allows the chuck
to be thermally decoupled from the X-Y table. The heads engage
releasably, in a vertically fixing manner, in suitable holding
members on the test substrate and as a result are in thermal
contact with the test substrate. They are connected to the holding
pins, which are secured to the X-Y table under spring force, so
that a vertical relative movement of the chuck can be utilized to
produce or release a nonpositive connection between the test
substrate and the chuck. On account of the fact that the holding
pins are secured to the X-Y table, they follow the movements of the
test substrate held on the receiving surface of the chuck.
[0025] According to a further advantageous embodiment of the
invention, the chuck comprises a chuck body with a chuck surface
and a chuck plate which rests on the chuck surface over its entire
area and can be released from the chuck body. This means that the
releasable chuck plate can be removed from the vacuum chamber in
order for the test substrate to be mounted on the chuck. The chuck
plate is connected to the chuck body in the same way as that
described above, via the thermally decoupling holding pins and
heads, with the corresponding holding means in this case being
present not on the test substrate but rather on the chuck
plate.
[0026] If, in a particular embodiment of the invention, the
directly and indirectly cooled parts of the chuck and of the
thermal radiation shield consist of material with a good thermal
conductivity, and the cooled parts of the chuck have highly
reflective surfaces, heat exchange with the surrounding, warmer
components through thermal radiation is minimized and heat exchange
with the parts to be cooled by heat conduction is optimized. The
use of a material with good thermal conductivity and a matt surface
for the thermal radiation shield ensures optimum dissipation of the
thermal energy which has been absorbed by the thermal radiation
shield.
[0027] In a further configuration of the invention, the chuck has a
heater on its underside, so that different temperatures than those
of the boiling point of the coolant used in each case can be set.
It is also possible to accelerate the process of heating up the
cooled chuck, for example in order for the test arrangement to be
changed.
[0028] To enable the thermal radiation shield to be incorporated in
the temperature regime of a heatable chuck, in a further
configuration of the invention the thermal radiation shield
likewise has a heater.
[0029] The invention is to be explained in more detail below with
reference to an exemplary embodiment.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1 shows a sectional view through a test apparatus
according to the invention, and
[0031] FIG. 2 shows a plan view of the thermal radiation
shield.
[0032] FIG. 3 is a cross-sectional partial view showing an
alternate arrangement for the probe holders.
DETAILED DESCRIPTION OF THE INVENTION
[0033] As illustrated in FIG. 1, a test apparatus for
low-temperature testing, known as a cryotest apparatus, has a chuck
1, which is connected to a chuck drive 2, preferably a motorized
X-Y table. The chuck 1 can be displaced in the working area by
means of the chuck drive 2. The working area is surrounded by a
vacuum chamber 3, which on one side has a loading opening 4, which
can be closed off in a vacuum-tight manner by a flap 5, and
centrally above the working area has an inspection opening 6, which
is closed off by quartz glass which reflects infrared radiation.
The working area is connected to a vacuum unit for evacuating the
working area.
[0034] The cylindrical chuck 1 consists of copper with a gold
coating, is connected to a coolant tank via the flexible coolant
line 7, and, depending on the coolant used, can be cooled to
various temperature ranges as a result of the coolant being passed
through passages 21 which are present in the interior of the chuck
1. The underside of the chuck 1 has a chuck heater 8.
[0035] The chuck 1 is secured to the chuck drive 2 by means of an
intermediate part 9 comprising a glass fiber tube which has a
slightly smaller cross section than the chuck 1 and a wall
thickness of approx. 1 mm.
[0036] Four first, mushroom-shaped holding rods 10 are secured to
the chuck 1 in such a way that they can execute small vertical
movements and engage into second, groove-like holding members 11 on
the substrate carrier 12. The groove-like holding members 11 enable
the substrate carrier to be inserted through an opening 4 of the
vacuum chamber with the substrate and possibly the probe holders 24
attached thereto. Rods 10 are fixed to the chuck drive 2 via a
holding pin 13 made from polymer fiber material and are held in a
lower position by springs 14. As a result of the heads 15 of the
first holding rods 10 engaging into the second holding member 11,
the first holding rods 10 are pulled by the second holding members
11 out of their lower position into an upper position, in which
they are held by by the second holding member 11, so that the force
of the springs 14 produces a defined clamping action onto the
substrate carrier 12 and good thermal contact is produced between
the receiving surface 16 of the chuck 1 and the underside of the
substrate carrier 12 and test substrate 17 held by the substrate
carrier 12.
[0037] A disk-like thermal radiation shield 18 with a ring-like
flanged edge 20 which is angled off downward and a probe holder 19
is arranged a short distance above the test substrate 17. The
thermal radiation shield 18, like the chuck 1, is connected to a
coolant tank via a flexible coolant line 7 and is cooled as a
result of the coolant being passed through passages 21 which are
present in the interior of the thermal radiation shield 18. The
thermal radiation shield is made from material with a very good
thermal conductivity and a highly reflective surface. As with the
chuck 1 a shield heater 22 is arranged on the thermal radiation
shield 18.
[0038] The temperature required to test the test substrate 17 is
controlled both at the chuck 1 and at the thermal radiation shield
18 by means of a measuring and control unit. The probe holder 19
forms the middle part of the thermal radiation shield and consists
of heat-storing material of very good thermal conductivity. A
circular through-opening 23 is arranged in the center, accurately
beneath the inspection opening in the vacuum chamber. This
through-opening 23 is closed off by a glass which reflects infrared
radiation.
[0039] FIG. 3 is a cross-sectional view showing an alternate
arrangement of the probe holders 25, 27 mounted on the heat shield
18 and connecting to substrate 17, which is mounted on substrate
carrier 12. The probe wires pass through a central opening in heat
shield 18.
[0040] While there have been described what are believed to be the
preferred embodiments of the invention, those skilled in the art
will recognize that other and further changes and modifications may
be made thereto without departing from the spirit of the invention,
and it is intended to claim all such changes and modifications as
fall within the true scope of the invention.
* * * * *